CMPSC 60: Week 4 Discussion

1. CMPSC 60: Week 4 Discussion Compiling and Makefiles

2. What is compiling • gcc steps • preprocessing – you know what this does • compilation – produces assembly code • assembly – creates an object file (.o) • linking – links .o files to create executable

3. gcc non-optional options • -c – compile but don’t link • -o – executable file name • -l<library> – link with library • -L<dir> – non-standard directory for libraries gcc -o taxman taxman.c -ltman -L <dir>

4. LIBRARY_PATH env. variable • Set the LIBRARY_PATH environment variable with (colon separated) directories • gcc will search these directories when looking for static libraries In csh (or .cshrc): setenv LIBRARY_PATH "/cs/student/cs60/test:cs/student/arun/libs" In bash (or .bashrc): export LIBRARY_PATH= "/cs/student/cs60/test:cs/student/arun/libs"

5. gcc optional options • -Wall – print lots of warnings • -W – print fewer (but sometimes different) warnings • -pedantic – strict ANSI C standard • -g – generate symbol table for debugging • -O<1-3> - compile with optimizations

6. Why we need Makefiles • Source files can be dependent on each other in very complicated ways. • Saves time of having to remember what to recompile, or recompile everything

7. Makefiles • Target • the name of a task – can be compiling a file, or a number of other things • Dependency • a target will often have dependencies • i.e. other targets that need to be done before it • A target is considered Up to date if it is more recent all files it depends on

8. Make tips • In a given target like: Build: gcc -o exe input.c helper.c space before the command is a single tab character • Examples..

9. Dependencies stimulate: stimulate.o inputs.o ouputs.o gcc -o stimulate stimulate.o inputs.o ouputs.o stimulate.o: stimulate.c gcc -c stimulate.c • stimulate.o, inputs.o, outputs.o are dependencies • If stimulate is not uptodate, tries to create it • Creates dependencies if needed • Dependencies can also be files

10. Abbreviations • $@ - full target name • $* - target name without suffix stimulate: stimulate.o inputs.o ouputs.o gcc -o stimulate stimulate.o inputs.o ouputs.o becomes stimulate: $*.o inputs.o ouputs.o gcc -o $@ $*.o inputs.o ouputs.o

11. Defines OBJECTS = stimulate.o inputs.o outputs.o stimulate: stimulate.o inputs.o ouputs.o gcc -o stimulate stimulate.o inputs.o ouputs.o becomes stimulate: $(OBJECTS) gcc -o $@ $(OBJECTS) CC = gcc CFLAGS = -g

12. Suffix rules .c.o: $(CC) $(CFLAGS) -c $< defines a suffix rule to create .o from .c When .o needed, can use this rule to create from .c

13. How to run make • Type make • Executes first target defined • Other targets can be executed as well by typing: • make <target> • If makefile is not called Makefile or makefile • make -f <makefile name>

14. Other handy make targets Target to build your executable – make sure to have this as the first rule all: <whatever you need> Target to get rid of all old files clean: rm -f *.o *~ #*# core* Make a brand new executable fresh: clean all

15. Write your own Makefile • Compile options: -g –Wall –pedantic –W • Needed libraries: -lm • Main file main.c and helper file that final executable depend on (helper.c)

16. Good solution CC = /usr/bin/gcc CFLAGS = -g -Wall -pedantic -W LIBS = -lm APP = basic OBJS = main.o helper.o all: $(APP) $(APP): $(OBJS) $(CC) $(CFLAGS) -o $(APP) $(OBJS) $(LIBS) main.o: $*.c gcc $(CFLAGS) -c $*.c helper.o: $*.c gcc $(CFLAGS) -c $*.c clean: rm -f *.o *~* $(APP)

17. Also works (because of default suffix rules) CC = /usr/bin/gcc CFLAGS = -g -Wall -pedantic -W LIBS = -lm APP = basic OBJS = main.o helper.o all: $(APP) $(APP): $(OBJS) $(CC) $(CFLAGS) -o $@ $(OBJS) $(LIBS) main.o: helper.o: clean: rm -f *.o *~* $(APP)